While the Commons debates today and tomorrow the contentious issues of human-animal hybrid embryos, same-sex parents and saviour siblings, all permitted by the new human fertilisation and embryology bill, overlooked in the general melee will be the bill's most dangerous innovation it would lift a ban in the HFE Act 1990 (pdf) against the genetic modification of human embryos. This would permit researchers here in the UK to try to alter the DNA that makes us human. Some enthusiasts applaud such a measure, seeing it as the first step towards bringing evolution under human control, but others (pdf) fear the complete commodification of children or even the rise of a genetically fixed two-tier society, as in the film Gattaca.

Are these hopes or fears excessive? After all, the bill prohibits implanting GM embryos in either human or animal wombs. The embryos are to be created "for research purposes" only. But what is the ultimate goal of such research?

You might think it's to prevent children from being born with genetic diseases. The fact is that we already know a considerable amount about how to do this. Couples who know they carry genes for a hereditary disease can have fertility treatment and their embryos screened, with only unaffected ones placed in the mother's womb, a less harrowing alternative to the older process of pre-natal testing and abortion of affected foetuses. They can use eggs or sperm from unaffected donors. They can adopt. They can choose to remain childless. In the case of some diseases, scientists are close to discovering ways of correcting genetic defects later in life, as has recently been done with one form of hereditary blindness.

So there is really no need to alter human embryos in order to combat genetic diseases. However, if the ultimate goal is to be able to learn safe ways of adding genes at will to human embryos to boost their intelligence, say to create true "designer children", then this tinkering is absolutely essential. Indeed, in the consultation document preceding the HFE bill, the government stated that its goal was the development of safe forms of human genetic modification.

More recently, the government's declared aims have been much more modest. They've claimed that such embryos might be useful for studying inherited disease. In fact, isolated cell cultures are far more powerful and convenient research tools.

The other principal reason the government gives when pressed on this issue is that altering embryos would help scientists to understand how they develop and implant in the womb. However, the law requires embryos to be destroyed before or at 14 days (when the nervous system begins to develop), too early to learn much, and as implantation continues to be prohibited, the bill itself undermines this reason. Or could the government have long-term plans to extend the 14-day limit or to permit GM embryos to be implanted, most likely when artificial wombs become available?

But most likely the government's real reason for allowing early experiments in altering the genes of human embryos is to allow UK scientists to establish a lead and claim intellectual property rights in basic techniques. We should not overlook the fact that Robert Winston and Ian Wilmut already hold patents on some methods that could be used to create genetically modified children.

But does the British public want GM children? Do members of parliament want to approve this measure without even properly debating it? If MPs don't wake up soon, they will set themselves up for a perfect storm of public opprobrium that will make the furore over GM crops the merest shower by comparison.